The present invention relates generally to combine harvesters and, more particularly, to a rotatable cleaning mechanism in combines for cleaning unwanted residue, such as chaff, straw, etc., from threshed grain.
Conventional cleaning systems clean threshed grain by blowing air through a set of planar sieves utilizing gravitational forces to urge cleaned grain through the sieve openings. With the advent of higher capacity threshing and separating mechanisms, such as rotary axial flow combines, the capacity for threshing grain has increased beyond the capacity of conventional cleaning systems to clean the grain. Accordingly, it is desirable to increase both the capacity and the efficiency of cleaning systems in combine harvesters so as not to limit the throughput capability of the combine.
The capacity and operating efficiency of conventional cleaning systems are significantly affected by the slope conditions under which the combine is operating, such as when the combine is harvesting crop on a hillside, because of the irregular distribution of the threshold, uncleaned grain on the cleaning sieves. Furthermore, conventional cleaning systems suffer from the disadvantage of being sensitive to any irregularities in the distribution of the flow of air across the cleaning sieves.
Some prior art rotary cleaning mechanisms continue to utilize gravitational forces to clean the threshed grain and, thus, do not greatly increase the capacity of the cleaning mechanism. Other prior art rotary cleaning devices do utilize centrifugal forces to increase their throughput capacity; however, such known devices have utilized frusto-conical sieves that are reciprocated in a direction parallel to the axis of rotation of the sieves. Such devices can be cumbersome, take up great amounts of space, and be subject to excessive vibrations due to the reciprocating movements of the conical sieves.